In copending, commonly assigned continuation-in-part application Ser. No. 945,842, filed on Sept. 26, 1978, and continuation-in-part application Ser. No. 27,740, filed on Apr. 6, 1979, there is disclosed a light regulation system which, among other things, is designed to utilize daylight and provide for a power related adjustable level of light. In the system disclosed in these applications, a control transistor operates in the saturated state thereof (full on) until the lamps are fired on and, once the lamps are fired, operates in the so-called linear region thereof from a minimum ("lamps on") current level until the current increases to the point where the ballast limits the current and the transistor is again saturated on. Examining the operation in more detail, a controlled DC level signal is provided at the base of each control transistor in the continuation-in-part application Ser. No. 27,740. When this signal is present, and during the period of time within each AC voltage half wave that the lamp(s) are not ignited, the control transistor is saturated "on" and only the ballast magnitizing current flows (in addition to lamp heater current when rapid-start lamps are employed). It is noted that in this condition, except for an approximate two volt drop in the transistor control circuit, all of the AC line voltage will appear across the primary of the ballast. Further, when the voltage across the lamp(s) rises within the half cycle, the lamps ignite, which changes the ballast's impedance. Because the control transistor was saturated "on" (with a base current greater than that required for the current flowing in the collector) the collector current begins to rise until a level is reached which corresponds to that required by the minority carriers flowing in the base region of the transistor. As the collector current begins to rise, the transistor begins to operate in the so-called linear region thereof and the voltage across the emitter-collector junction increases to the extent of any "excess" voltage. This excess voltage corresponds to the difference between the AC line source voltage and the voltage level the ballast "complied" to in order to supply the transistor limited level of ballast current. In this regard, it is noted that these systems are so-called voltage compliance systems wherein the voltage complies to a current level (in lieu of the current complying to the AC line voltage source).
As is explained in more detail below, the amplitude controlled current technique provided by the systems of the previous applications is dissipative in nature and, in a specific example, the power consumed by the control unit varies up to almost 20 watts at an approximately 90% power input.